code: def test_duplicate(self):
      # Verify the `duplicate()` method works with a `PretrainedTransformerIndexer` in
      # a `TextField`. See https://github.com/allenai/allennlp/issues/4270.
      instance = Instance(
          {
              "words": TextField(
                  [Token("hello")],
                  {
                      "tokens": PretrainedTransformerIndexer(
                          "bert-base-uncased"
                      )
                  },
              )
          }
      )
  
      other = instance.duplicate()
      assert other == instance
  
      # Adding new fields to the original instance should not effect the duplicate.
      instance.add_field("labels", LabelField("some_label"))
      assert "labels" not in other.fields
      assert other != instance
  
file_path: allennlp/tests/data/instance_test.py
imports: import numpy
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.data import Instance
  from allennlp.data.fields import TextField, LabelField, TensorField
  from allennlp.data.token_indexers import PretrainedTransformerIndexer
  from allennlp.data.tokenizers import Token
label_desc: Use image node_id 2 for calling the TestInstance obj's underlying member method code with example usage: obj.test_duplicate() without return types